May 4, 2012
11:00 AM (EDT)

News Release Number: STScI-2012-22

Hubble to Use Moon as Mirror to See Venus Transit

May 4, 2012: This mottled landscape showing the impact crater Tycho is among the most
violent-looking places on our Moon. Astronomers didn't aim NASA's Hubble
Space Telescope to study Tycho, however. The image was taken in preparation
to observe the transit of Venus across the Sun's face on June 5-6.

Hubble cannot look at the Sun directly, so astronomers are planning to point the
telescope at Earth's moon, using it as a mirror to capture reflected sunlight and
isolate the small fraction of the light that passes through Venus's atmosphere.
Imprinted on that small amount of light are the fingerprints of the planet's
atmospheric makeup. These observations will mimic a technique that is already
being used to sample the atmospheres of giant planets outside our solar system
passing in front of their stars. In the case of the Venus transit observations,
astronomers already know the chemical makeup of Venus's atmosphere, and
that it does not show signs of life on the planet. But the Venus transit will be used
to test whether this technique will have a chance of detecting the very faint
fingerprints of an Earth-like planet, even one that might be habitable for life,
outside our solar system that similarly transits its own star. Venus is an excellent
proxy because it is similar in size and mass to our planet.